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Enantioselective Hydrosilylation of Acetophenone with RhodiumThiazolidine Catalysts.

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by the complexes [(C8Hs)Ti]zCsHsand [(C5H5)CoI2CsH8,
whose bridging CsHs rings are, however, nonplanar"]. The
second, synfacial variant is realized in [(CsHs)Cr]zCsHs
lrZai
as well as in the complex [(C5H5)v2CsHs2, which we
prepared from VC12, NaC5H5, and K2CsHs[2b1.A compound 3 having the analogous composition to 2,
[(C5HS)Cr]2C8Hs,
was previously synthesized using another
method [(C5H&Cr NazCsHs] and characterized by X-ray
~rystallography[~"].
Surprisingly, in 3 a C8 chain occurs,
whose terminal C atoms are o-bonded to the Cr atoms.
+
/\\
A metal-metal bond order of 2 would also result from
the interaction of two chromocene moieties of individual
electron configuration ... (eZ;xy,x2- ~ ' ) ~ ( ;z2)'
a , ; the different overlap qualities of the ez and a , orbitals in 4 imply
an MO sequence which-occupied by 2 x 4 electronsleads to the configuration (e2)4(a1)2(aT)2
for 4. This is corroborated by the finding that the radical cation 4'@, generated electrochemically from 4, has an orbitally non-degenerate ground state [(g) (dimethoxyethane, 27 "C) = 2.024,
a(53Cr)not resolved]. Finally, the formation of 4 as a resonance hybrid secures that in each of the two canonical
forms one Cr atom has an 18e shell.
Received: December 13, 1982 [Z 222 IE]
German version: Angew. Chem. 95 (1983) 319
2
1
3
By allowing CrCI2.THF to react with NaCsHS and
KzC8Hs[4]we have now obtained compound 4 which, according to its elemental analysis and mass spectrum, also
has the composition Cl8HlSCr2but which, in contrast to 3,
is characterized by simple NMR spectra [4 ([Ds]toluene,
27 "C); 6('H)=4.22 (s, lOH), 3.89 (s, 8H); 6(I3C)=74.53,
86.551. The X-ray structure analysis reveals that 4 has an
analogous structure to 2, and is hence an isomer of 3 (Fig.
1y3bl.
Fig. I . Structure of 4 in the crystal (ORTEP representation, thermal vibrational ellipsoids with 30% probability). Mirror plane perpendicular to the
Cr-Cr axis. Space group Pnma, a = 1184.9(3), b = 1577.8(3), c = 764.1(2) pm,
Z=4. R,=0.052 (weighting w =2.6/&,) for 693 independent reflections
( I > 2 a ; CAD4, Enraf-Nonius, M o k ) . Important bond lengths [pm]: Cr-Cr'
239.0(2), Cr-CII 226(1), Cr-C12 207(1), Cr-C13 210(1), Cr-C14 205(1),
Cr-CIS 225(1), Cr-C21 220(1), Cr-C22 221(1), Cr-C23 219(2), Cr-C24
217(2), Cr-C25 220(2), Cll-C12 142(1), C12-CI3 141(2), C13-CI4 139(2),
C14-CI5 144(1), C11.. .C15 310(2). Angles between the "best planes": at
C(ll)-C(15) axis: 131.4". between C(l1--15) and C(21-25): 16.2". Distances Cr-C( 1 1 - 15) 149 pm, Cr-C(21-25) 186 pm. Further details on the
crystal structure investigation can be obtained from the Fachinformationszentrum Energie-Physik-Mathematik, D-75 14 Eggenstein-Leopoldshafen,by
quoting the depository number CSD 50382, the names of the authors and the
journal citation.
4 can be considered as a combination of two "halfopen" chromocene molecules[5a1,5 , which share the atoms
Cll-C15. The dinuclear complex 4, which as opposed to
the paramagnetic monomer chromocene (S = 1) is diamagnetic, displays a bond distance d (Cr-Cr) = 239 pm. Compared to other species with Cr-Cr bonds[sb1,this distance
suggests a Cr=Cr double bond.
[I] J. W. Lauher, M. Elian, R. H. Summervitle, R. Hoffmann, J. Am. Chern.
SOC.98 (1976) 3219 and literature cited therein.
I21 a) D. J. Brauer, C. Kriiger, Inorg. Chem. 15 (1976) 2511; b) C. Elschenbroich, J. Heck, W. Massa, E. Nun, R. Schmidt, J . Am. Chem. Sor.. in
press.
[3] a) W. Geibel, G. Wilke, R. Goddard, C. Kriiger, R. Mynott, J . Organomef.
Chem. 160 (1978) 139; b) Thermal rearrangement of 3 also leads to
isomer 4 (cf. G. Wilke in M. Tsutsui: Fundamental Research in Homogeneous Catalysis, Vol. 3, Plenum, New York 1978, p.'1; R. Goddard, C.
Kriiger in P. Coppens, G. Hall: Elecfron Distributions and the Chemical
Bond, Plenum, New York 1982, p. 297.
[4] Procedure: A solution of KZCaHs(2.0 g, 11 mmol) in 100 mL tetrahydrofuran (THF) is added to a stirred suspension of CrCI2.THF (4.39 g, 22.1
mmol) in 120 mL T H F at -25 "C, and after 30 min solid NaCSHs (1.9 g,
22 mmol) added. After warming to room temperature and 2 h refluxing,
the solvent is removed and the residue sublimed at
mbar. The first
fraction (60 "C) contains a mixture of chromocene and q5-cyclopentadienyl-$cyclooctatetraenechromium
(1.92 9). Extraction of the second
brown-red fraction (140°C) with 50 mL petroleum ether 40/60 and crystallization (1 week at 4°C) leads to the complex 4 as black needles (185
mg (4.9%), decomp. > 180 "C) €1-MS [ m / r (%): 339 (10.2) ( M + I ) + , 338
(17.9) M +,221 (25.8) (M-CsHsCr)+, 195 (12.7) C , , H , , C r + , 182 (65.6)
CloHloCr+,117 (100) C5H5Cr+etc.
[5] a) "Open" chromocene: D. R. Wilson, JLZ. Liu, R. D. Ernst, J . Am.
Chem. SOC.104 (1982) 1120; U. Giannini, E. Pellino, M. P. Lachi, J. Organomet. Chem. I 2 (1968) 551; b) cf. F. A. Cotton, R. A. Walton: Multiple
Bonds Between Metal Afoms. Wiley, New York 1982, and literature cited
therein.
Enantioselective Hydrosilylation of Acetophenone
with Rhodium/Thiazolidine Catalysts**
By Henri Brunner*, Georg Riepl. and Helgard Weitzer
We recently reported on the enantioselective hydrosilylation of prochiral ketones with (cod)=-pyridine imine
catalysts (cod = 1,5-~yclooctadiene)~~~.
With the catalyst
system [ ( c ~ d ) R h C l ] ~(Rh
/ l : 1 = I : 13) an enantiomeric excess (ee) of up to 57.3% was achieved in the reaction acetophenone-c 1-phenylethanol (substrate :Rh = 110 :1)[l1.
With catalyst systems whose pyridine imine component
is obtained from (-)-3-aminomethylpinane and 2-pyridine[*] Prof. Dr. H. Brunner, G. Riepl, H. Weitzer
Institut fur Anorganische Chemie der Universitat
Universitatsstrasse 3 1, D-8400 Regensburg (Germany)
[**I Asymmetric Catalyses, Part 10. This work was supported by the
6n
4n
4n
6n
4
Angew. Chem. Int. Ed. Engl. 22 (1983) No. 4
5
Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and BASF AG.-Part 9: see Ref. 111.
0 Verlag Chemie GrnbH, 6940 Weinheim, 1983
0570-0833/83/0404-0331 $02.50/0
33 I
carbaldehyde, the ee value can be increased to 78% (substrate :Rh= 100 : 1, Rh :ligand= 1 : IS); L-valine methyl ester and L-alanine methyl ester as amine components in the
Schiff base condensation, respectively, yield only slight or
no enantiomeric excess. The best catalyst system for the
model reaction is obtained from [(cod)RhCI], and 2, the
[2] H. Beckett, G. R. Jones, Tetrahedron 33 (1977) 3313; H. Abdallah, R.
Gree, R. Carrie, Tetrahedron Lett. 23 (1982) 503; P. N. Confalone, G. PizI
.
Am. Chem. SOC.
zolato, E. G. Baggiolini, D. Lollar, M. R. Uskokovic, .
99 (1977) 7020.
A Novel Planar Antiaromatic Dibenzo[8]annulene**
By Heinz Durr*, Gunter Klauck. Karl Peters, and
Hans Georg von Schnering
Dedicated to Professor Georg Wittig
condensation product of L-cysteine methyl ester and 2-pyridinecarbaldehyde. With the Rh/thiazolidine system an
enantiomeric excess of up to 86.7% is achievable (Table
1)-
Cyclopropene double bonds are intermediary in character between the normal olefinic CC double bond and the
CC triple bond. For this reason dibenzo[a,e]dicyclopropa[c.g]cyclooctene 2 , a cyclooctatetraene derivative in
which two >C=C< units are each replaced by a cyclo-
Table 1. Enantioselective hydrosilylation of acetophenone with diphenylsilane without solvent. Catalyst system: [(cod)RhCl]~/Z.The (R)-enantiomer is
always formed as main product.
T Wl
Rh/Z
Rh/
Substrate
1/9
1/5
1/2
1/1.6
1/5
1/5
1/5
1/210
0-20
1/210
0-20
1/210
0- 20
0-20
0-20
0-20
0-20
0-20
- 10
- 15
1/5
1/5
1/9
1/210
1/860
1/1220
1/1710
1/28M)
1/210
1/210
f
fhl
38
20
20
43
65
40
65
40
115
235
Yield
Chem. [%I
Opt. 1% eel
99
96
96
9s
94
93
92
43
19
98
83.2
80.0
74.7
72.3
78.2
75.0
78.9
73.6
83.6
86.7
The Rh/thiazolidine system is also far superior to the
Rh/Schiff base systems with regard to reaction rate and
stability. High enantiomeric excesses are possible with the
pyridine imine ligands only at substrate-rhodium ratios of
up to 200 : l['I; in contrast, the Rh/thiazolidine catalyst
leads to high conversion and high enantiomeric excess under the same conditions at substrate-rhodium ratios of up
to 2000 :1 (Table 1).
In the condensation of 2-pyridinecarbaldehyde with 1phenylethylamine, 3-arninomethylpinane, alanine methyl
ester and valine methyl ester, Schiff bases are formed
which show characteristic low chemical shifts of the proton of the CH=N group in the 'H-NMR spectrum
(6 = 8.0-8.7). The 'H-NMR spectrum of the thiazolidine
derivative 2 exhibits two doublets for the CHSN protons
at 6 = 5.84 and 5.66 (35HH
= 11.4 Hz), in the intensity ratio
58:42; this finding is attributed to the presence of two
diastereomers (the (2R,4S)-diastereomer is shown in the
formula), which differ only in the configuration at C2. The
diastereoselectivity in the formation of 2 corresponds to
that in the oxazolidine ring closure of aldehydes and ephedrine['I. It is surprising that an almost stereospecific synthesis of 1-phenylethanol is possible with a 58 :42 diastereomeric mixture of the thiazolidine 2 and [(cod)RhClIz.
Received: November 24, 1982 [Z 209 IEI
German version: Angew. Chem. 95 (1983) 326
The complete version of this communication appears in:
Anaew. Chem. St_.
c~d1983. 445-450
[I] H. Bmnner, G. Riepl, Angew. Chem. 94 (1982) 369; Angew. Chem. Inr.
Ed. Engl. 21 (1982) 377; Angew. Chem. Suppl. 1982, 769.
332
0 Verlag Chemie GrnbH, 6940 Weinheim, 1983
3
2
1
propene ring, should be ranked between the olefinic dibenzo[a,e]cyclooctene 1 and the antiaromatic"' [8]annulene
3[41.Compound 3 is planarf5]and relatively stable (transannular interactions see @I).
We have checked, 1) whether the cyclopropene rings in
2 enforce a planar structure on the framework of 1; 2) to
what extent the planarity in 2 renders an antiaromatic
[Slannulene possible.
For the synthesis of 2 the diyne 3 was first allowed to
react with the diazo compounds 4a-d to give the bis-3Hpyrazoles 5a, b and the bis(spiro-3H-pyrazoles) 5c, d.
R R'
x
5
R
I
R'
a
b
c
d
CH,
CH,
CoHs
C6HS
-o-C6H4-o-C6H4-o-C6H4-CO-o-C6H4-
I
5
Yield
[%I
M.p.
["c]
24
65
46
64
340
135
175
120
Yield
2
[%I
M.p.
["c]
8.7
153
Yield
[%I
1.8
16
20
M.p.
["c]
135
230
120
[*] Prof. Dr. H. Durr, G. Klauck
Fachbereich 14, Organische Chemie der Universitat
D-6600 Saarbriicken (Germany)
Prof. Dr. G. von Schnering, Dr. K. Peters
Max-Planck-Institut fur Festkorperforschung
Hersenbergstr. I , D-7000 Stuttgart 80 (Germany)
I**] Photochemistry of Small Rings, Part 42. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.-Part 41: E. Liiddeke, H. Rau, H. Diirr, H. Schmitz, Tetmhedron 33 (1977) 2677.
OS70-0833/83/0404-0332 $02.50/0
Angew. Chem. Int. Ed. Engl. 22 (1983) No. 4
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rhodiumthiazolidine, acetophenone, enantioselectivity, catalyst, hydrosilylation
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